1. Field of the Invention
The invention pertains to the field of biofuel production. More particularly, the invention pertains to biofuel compositions containing nitrile moieties and methods for production thereof.
2. Description of Related Art
Recently, as petroleum stocks dwindle, much emphasis has been given to the development of biofuels. In particular, alcohol is blended with naphtha to make gasohol, or is chemically bound to fatty acids to produce biodiesel. Conventional biodiesel is a fatty acid ester of lower alcohols, methanol in particular (and ethanol to a lesser extent), the former, known as fatty acid methyl ester is abbreviated FAME. One advantage of FAME relative to commercial diesel (from petroleum) is its negligible sulfur content, the presence of which contributes to acid rain formation. An additional advantage of FAME is its excellent lubricity, which is superior to that of commercial diesel fuel. Ironically, the little lubricity found in the commercial diesel fuel is directly linked to the presence of sulfur contaminants, and thus as levels of sulfur diminish, so does the internal lubricity of the fuel. In some parts of the world 0.3% sulfur is still acceptable, although that is still highly polluting. Biofuels compositions of the present invention also have essentially no sulfur content and thus their combustion does not contribute to acid rain.
Black exhaust smoke is another known problem of commercial petroleum diesel fuels, and is directly related to the nature of the hydrocarbons found in the fuel. Hydrocarbon fractions have both aromatic and aliphatic components, and the former contribute significantly to the formation of black smoke and soot. Aromatic hydrocarbons are found in all commercial diesels, yet are totally absent in biofuels like FAME. Not only do aromatics produce more smoke, but they also reduce the quality of diesel fuel by lowering the cetane index. Biofuels produce a lesser amount of smoke.
Cetane Index is a measure the speed of combustion by auto-ignition under pressure and is of importance in the quality of diesel fuel. The higher the Cetane index, the faster the combustion, and the higher the mechanical work output. Indices of 40 and 45 are the present minimums acceptable in the US and Europe, respectively. Most biofuels, however, are closer to the 60 mark, including FAME and the novel nitrile biofuels covered in the present invention. Cetane index in commercial diesel fuels can vary substantially, depending on their sources, which are quite diverse. In general, higher percentages of aliphatic hydrocarbons gives a higher cetane index, and the reverse is true for higher percentages of aromatic hydrocarbons.
Viscosity and liquid range are two additional factors that affect the quality of diesel fuels. Preferably, fuel intended for diesel motors has a viscosity under about 10 centistokes (ctsk), and a liquid range broad enough to prevent freezing of fuel lines in the winter. Diesel injectors work against tremendous internal cylinder pressure, and proper fluidity in fuel lines is therefore important. This is one reason why natural oils cannot be employed directly, and are instead modified through chemical reactions to provide derivatives with proper viscosity and liquid ranges.
First Generation Biodiesel
Renewable fuel of the FAME type is the generic biodiesel known to most people, and is commonly made by a transesterification reaction involving triglycerides and lower alcohols like methanol and ethanol. The method appeared in the patent literature about two decades ago, specifically in U.S. Pat. Nos. 4,164,506 and 4,695,411, as well as in a number of chemical publications, for example Dorado, Ballesteros et al, Energy and Fuels, 17(6), 1560 (2003). To this date there is ongoing research in the area of fatty acid esterification for fuel applications. In transesterification reactions, triglycerides of olive, soybean, sunflower, and palm oils react with lower alcohols in alkaline medium (S. Bhatia et al, Energy and Fuels, 18(5), 1555 (2004)). Transesterification is a relatively complex process (M. P. Dorado et al., Energy and Fuels, 18(1), 77 (2004)) in which several side reactions can affect yields in an adverse way. The fundamental reaction involves replacement of a glycerin group by lower alcohols, (S. G. Wildes, Chemical Innovation, May 2001, p. 23). The net reaction is shown below as the transesterification of a fatty (R) triglyceride with methanol:

The reaction product is the fatty acid methyl ester RCOOOCH3, or FAME, along with glycerin formed as a by-product. FAME type biodiesels are regarded as the first generation of such renewable fuels, commonly known as “biodiesel”.
Acceptance of biodiesel is still a gradual process. Supply is constrained by the chemistry in transesterification, which is largely a batch operation. This fuel is being used in public transportation, some trucks, and farm equipment, and is usually blended with petroleum diesel. The US armed forces use large amounts of biodiesel, as a 20% blend in petroleum diesel, called B20 (M. McCoy, C&ENews, Feb. 21, 2005, p 19).
Second Generation Biodiesel
At this time there is a second generation of biodiesel under development. The process involves the pyrolysis of triglycerides, which can be conducted jointly with crude oil refining. The Resulting fatty carboxylic acids can be esterified directly, yielding esters akin to FAME through acid-catalyzed direct esterification (N. Irving, Guatemalan Patent Application A2006,0473) as shown in Equation 2 below:

Methanol is the preferred alcohol for steric reasons. The resulting products are considered hybrid fuels.
In a more recent work (US Pat. Application 2007/0007176 A1) researchers used catalytic pyrolysis to promote decarboxylation of fatty acids resulting from pyrolysis of triglycerides. Pyrolysis is conducted at temperatures between 350 and 400° C., and CO2 is described as a by product. A difference between these two processes is that in the first case acrolein is generated during triglyceride pyrolysis. In the process of the '176 application work neither glycerin nor acrolein are mentioned as being by products.
Despite the advantages described above, FAME type fuels are deficient in energy content in comparison to petroleum diesel fuels. The ester functional group of FAME contains a highly oxygenated carbon atom. This functional group contributes appreciable weight to the molecules, but it does not contribute significantly to the energy output of the fuel during combustion since the ester carbon is already in the oxidation state of CO2. Thus there exists a need for a biofuel that retains the advantages of FAME, but which has a high energy content similar to petroleum derived fuels.
The present invention also pertains to methods for producing fatty aliphatic nitrile compositions from oleaginous feedstocks. Methods are known in the art for the production of aliphatic nitrites, however, none of the known methods are suitable for the large scale production of fatty aliphatic nitrites. One known route to nitrile compounds is by conversion of amides. The amide function —CONH2 can undergo dehydration leading to the formation of a nitrile moiety along with loss of one water molecule. It is possible to conduct amide dehydration under atmospheric pressure, although only with great difficulty, requiring special conditions like flash pyrolysis or exceptionally strong dehydrating agents. A classic example is the formation of acetonitrile by dehydration of acetamide using phosphorous pentoxide as the dehydrating agent (Equation 2B) in a constant distillation process under atmospheric pressure as the reagents are heated (A. Vogel, Practical Organic Chemistry, prep. III, 111, Longmans, Green and Co., London).

This method would not be industrially viable in the present case due to the cost of phosphorous pentoxide, which is employed in relatively large quantities. It would be very expensive to prepare fuels and solvents in bulk quantities by this method.
Compounds with carboxylic functionalities can be derivatized with the nitrile function by other known methods, none of which is viable in an industrial scale (see J. March, Advanced Organic Chemistry, 3rd Edition, Wiley-Interscience, New York, 1985).
For example: Nitriles have been formed by treating carboxylic acids with trifluoroacetic acid anhydride and sodium nitrite. Alkali carboxylic acid salts have been treated directly with cyanogen bromide BrCN, and the intermediate formed decarboxylated to form the corresponding nitrite. Carboxylic acid esters, have been treated with an aluminum dialkyl amide (e.g. (CH3)2AlNH2), to yield nitrites directly. Finally, a carboxylic acid chloride can react with ammonia forming the amide which can then be dehydrated as described above. Even though each of these methods allows conversion of a carboxyl derivative into a nitrile moiety, none of them is suitable for efficient industrial nitrile production from fatty acids. The present invention provides methods which can effectively convert fatty acid feedstocks into aliphatic nitrile compositions on a substantial scale.